In the machining of workpieces in machining centers a number of successive operations are performed, starting with reaming and ending with fine drilling.
The required tools are for the most part interchanged automatically. During the interchange, errors of greater or lesser magnitude occur statistically which can be attributed to various causes:
When the tool is being attached to the cutting position on the machine shaft a displacement of the axle or a faulty angle setting (tilting) may occur between the machine axle and the axle of the adjusting tool.
A similar faulty axle or angle setting may occur at other disconnecting points of the tool.
Errors can also be caused by dirt at the cutting positions and disconnecting points.
When the cutting inserts are being clamped in position or the cutting parts are being fixed in their carriers the clamping or fixing may be faulty.
In addition, systematic wear errors occur and cause a gradual reduction of the drilling diameter. Especially in soft workpieces, a built-up edge may form which is due to the deposit of metallic particles on the edge during machining, with a resulting change in the edge's geometry. In addition, there are fatal errors which make it necessary to replace a tool, such as breaking of the edge and cutting inserts being left out of the tool components or coming loose from them.
All these errors produce variation in both the drilling diameter and in the quality of the drilling. Previously there was no easy way of detecting these errors before machining had actually taken place. This is particularly true of jointing and tolerance errors which do not exceed certain limits of accuracy. These errors could only be detected by checking the results of the drilling (post-process checking), for example, by the use of sensors to measure the workpiece directly, and were the cause of undesirable defective goods.
It is moreover known with respect to precision-adjustment heads (EP-B 0 491 724) how to adjust the radius of a cutting edge at the toolhead to a set predetermined drilling diameter within a tolerance range either manually or, for example, by means of an adjustment motor. The potential accuracy of precision-adjustment heads could not be fully accounted for by the statistically occurring errors, especially in machining centers.
In the light of the foregoing, the purpose of the invention is to develop a process and a device which will make it possible to detect and compensate for statistical jointing and wear errors in fine drilling before the process starts.
In claims 1 and 13 combinations of characteristics are proposed for the accomplishment of this purpose. Advantageous embodiments and additional forms of the invention will be found in the subclaims.